Rapid cure silicone lubricious coatings

ABSTRACT

Novel, lubricious coatings for medical devices are disclosed. The coatings provide improved lubricity and durability, and are readily applied in coating processes. The present invention is also directed to a novel platinum catalyst for use in such coatings. The catalyst provides for rapid curing, while inhibiting cross-linking at ambient temperatures, thereby improving the production pot life of the coatings.

This application is a divisional application of U.S. application Ser.No. 16/052,856 filed Aug. 2, 2018, now U.S. Pat. No. 11,224,869, whichis a continuation of co-pending U.S. application Ser. No. 15/272,538filed on Sep. 22, 2016, now abandoned, which is a divisional of U.S.application Ser. No. 15/232,085 filed on Aug. 9, 2016, now U.S. Pat. No.10,441,947 issued on Oct. 15, 2019, which is a divisional of U.S.application Ser. No. 13/296,771 filed on Nov. 15, 2011, now U.S. Pat.No. 9,434,857 issued on Sep. 6, 2016; the entire disclosures of whichare hereby incorporated herein by reference for all purposes.

TECHNICAL FIELD

The field of art to which this invention pertains is silicone-basedlubricious coatings, in particular, silicone-based lubricious coatingsfor use on medical devices.

BACKGROUND OF THE INVENTION

Lubricious coatings are typically required for implantable or insertablemedical devices such as hypodermic needles, surgical needles, catheters,and cutting devices that contact tissue. The primary purpose of suchcoatings is to ease the penetration or insertion of the device into andthrough tissue, thereby facilitating a procedure.

A number of conventional, biocompatible lubricants have been developedfor such applications, and they are typically silicone (e.g.,polydimethylsiloxane) or silicone-containing coatings. For example,condensation-cured silicone coatings are known to be useful aslubricious coatings on medical devices. Such coating formulationscontain amino and alkoxyl functional groups, which can be cured(cross-linked) at relatively low temperatures and high humidity levels.It is also known to use an aminopropyl-containing silicone as alubricious coating for syringe needles. Those coatings use anepoxy-containing silicone as a cross-linking agent and may have improvedpenetration performance with multiple penetrations. It is also known toutilize thermoplastic polymers such as polypropylene (e.g., in powderform) in blends of silicone solutions to improve the mechanicalproperties of the resulting coating layers. The polypropylene powdersmay increase the durability of silicone needle coatings withoutsacrificing lubricity. Most of the known and conventionally usedsilicone coatings listed above require a lengthy thermal curing stepafter application, which is quite often unsuitable for rapid, high speedproduction processes.

Attempts have been made to improve coating cure times including rapid UVcurable silicone lubricious coatings that can be cured rapidly (<10seconds) on a medical device, such as needle, after UV light exposure.However, the potential hazard of certain UV curable components typicallycontained in such coatings may provide cause for concern.

Karstedt of GE Silicone invented a highly active platinum catalyst forhydrosilylation at the beginning of the 1970's (U.S. Pat. No.3,775,452). The “Karstedt catalyst” is highly active at ambienttemperature, and this quality makes it difficult to use in mostcommercial silicone coatings without the addition of an inhibitor.Several other platinum catalysts had been subsequently inventedattempting to address this problem. For example,platinum-cyclovinylmethylsiloxane complex was made immediately after theinvention of the Karstedt catalyst (U.S. Pat. No. 3,814,730), and thiscatalyst is purported to provide longer production process pot life fora vinyl/hydride reactive coating solution mixture. Platinumtetramethyldivinylsiloxane dimethyl maleate and platinumtetramethyldivinylsiloxane dimethyl fumarate were disclosed in themid-1990's, both of which are claimed to provide longer productionprocess pot life for vinyl/hydride coating solution mixtures. Each ofthose catalysts is still commonly used in the silicone coating industry.

In order to be useful on medical devices such as surgical needles, it iscritical that lubricious silicone coatings be durable and easy to applyin a uniform, consistent manner. A surgical procedure in which tissue isapproximated or closed with surgical sutures typically requires multiplepasses of the surgical needle and suture through tissue. Ease ofpenetration over multiple passes through tissue will make the surgeon'sjob easier and this will likely result in a better tissue repair orclosure. The patient will benefit not only by enhanced healing andsuperior outcome, but also by a faster procedure resulting in a shortertime for possible exposure of the wound or opening to pathogens in theenvironment, and also requiring a shorter period of time that thepatient is under general anesthesia, when anesthesia is required.

Surgical needles are typically manufactured in high speed productionprocesses. For example, U.S. Pat. No. 5,776,268, incorporated byreference, discloses such processes. After the needles are formed andshaped (typically from wire stock), the in-process needles are cleaned,and the needles are coated with lubricious coatings in a conventionalmanner such as by dipping, spraying, brushing, etc. After application ofthe coatings in a uniform manner to substantially coat the exteriorsurfaces of the needles, the needles are then moved into appropriatecuring equipment, such as an oven, for a coating curing process whereinenergy (e.g., thermal) is provided to cure the silicone coatings.

Silicone coatings are typically prepared at the manufacturing site bymixing the silicone polymer components with a suitable catalyst andsolvents. Such coatings and catalysts, especially when of medical gradefor use on medical devices, are expensive and typically have what isconventionally known in this art as a short “pot life”. The term potlife, as conventionally used in the art, has the meaning that thesilicone coatings when mixed with catalyst and ready for application ina coating process typically have a limited amount of time in which theyare useful because of cross-linking that occurs at ambient conditions inthe production facility. Such short pot life can result in a number ofknown problems, including for example, premature curing, leading to aviscosity increment of the coating solution during the time of itsusage. This will typically cause inconsistencies in the resultingcoating on the surface of the medical device, resulting in both visualand performance deficiencies.

There is a need in this art for improved silicone coatings for medicaldevices that have improved lubricity and durability for multiple passesthrough tissue. There is also a need for improved silicone coatings thathave improved cure times without sacrificing lubricity and durability,and which do not contain potentially harmful ingredients.

There is a further need in the art for improved catalysts for siliconecoatings that provide for rapid curing when exposed to heat but whichare relatively stable in a silicone coating solution over time atambient conditions and for extended periods of time in typicalproduction environments.

SUMMARY OF THE INVENTION

Accordingly, novel lubricious silicone coating compositions aredisclosed. The coating compositions contain a first cross-linkablesilicone polymer having reactive functionalities, a siloxanecross-linking agent, and a second non-cross-linkable silicone polymer.The second non-cross-linkable silicone polymer has a weight averagemolecular weight greater than about 200,000, preferably about 260,000 toabout 10,000,000. The coating compositions may also contain a platinumcatalyst.

Another aspect of the present invention is a medical device having asurface, wherein at least part of the surface is coated with theabove-described novel silicone coating composition.

Yet another aspect of the present invention is a method of coating amedical device with a silicone, lubricious coating composition. In thenovel method of coating the medical device, a medical device is providedhaving a surface. A lubricious silicone coating is applied to at leastpart of the surface. The coating composition contains a cross-linkablesilicone polymer and a non-cross-linkable silicone polymer, wherein thepolymer has a weight average molecular weight greater than about200,000, preferably about 200,000 to about 10,000,000. The coating alsocontains a silicone cross-linking agent and a catalyst.

Still yet another aspect of the present invention is a novel platinumcatalyst for use with cross-likable silicone coatings. The catalystconsists of a platinum complex having the following formula:Pt[(CH₂═CH)(Me)₂Si]₂O.C₆H₁₀(OH)(C≡CH)

A further aspect of the present invention is a method of curing across-linkable silicone polymer containing coating solution using theabove-described catalyst.

These and other aspects and advantages of the present invention willbecome more apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

The terms silicone and siloxane are conventionally used interchangeablyin this art, and that usage has been adopted herein

Lubricious Coating Composition

The present invention is directed to novel lubricious silicone coatingcompositions which are particularly useful for coating surfaces ofmedical devices such as surgical needles and other tissue piercing orcutting devices. The compositions include a mixture of a cross-linkablesiloxane polymer and a non-cross-linkable siloxane polymer, aconventional silicone cross-linking agent, and a platinum catalyst. Thesilicone polymer components are blended with conventional aromaticorganic solvents, including, for example, xylene and aliphatic organicsolvents (such as, for example, hexane or its commercial derivatives) toform coating solutions or compositions.

The cross-linkable siloxane polymers useful in the coating compositionsof the present invention will have reactive functionalities or terminalfunctional groups, including but not limited to vinyl terminated,hydroxyl and acrylate functional groups. The cross-linkable siloxanepolymers that can be used in the lubricious coatings of the presentinvention preferably include vinyl terminated polydialkylsiloxane orvinyl terminated polyalkoarylsiloxane. Examples include but are notlimited to the following vinyl terminated siloxane polymers:polydimethyl siloxane, polydiphenylsilane-dimethylsiloxane copolymer,polyphenylmethylsiloxane, polyfluoropropylmethyl-dimethylsiloxanecopolymer and polydiethylsiloxane. It is particularly preferred to usevinyl terminated cross-linkable polymethyl siloxane.

The non-cross-linkable siloxanes that can be used in the practice of thepresent invention include polydimethyl siloxane,polyalkylmethylsiloxane, such as polydiethylsiloxane,polyfluoropropylmethylsiloxane, polyoctylmethylsiloxane,polytetradecylmethylsiloxane, polyoctadecylmethylsiloxane, andpolyalkylmethyl dimethylsiloxane, such aspolyhexadecymethylsiloxane-dimethyl siloxane. It is particularlypreferred to use non-cross-linkable polymethyl siloxanes with weightaverage molecular weights (Mw) greater than 200,000, preferably about200,000 to about 1,000,000, which are in the form of non-flowable gumhaving a viscosity greater than 600,000 cps.

The cross-linking agents that can be used in the coatings of the presentinvention include conventional silicone cross-linking agents such as,for example, polymethylhydro siloxane,polymethylhydro-co-polydimethylsiloxane, polyethyhydrosiloxane,polymethylhydrosiloxane-co-octylmethylsiloxane,polymethylhydrosiloxane-co-methylphenylsiloxane. One preferredconventional catalyst for use in the coatings of the present inventionis polymethylhydro siloxane. Precise control of cross-link density inthe coatings of the present invention is achieved by precise control ofthe ratio of non-cross-linkable silicone polymer (e.g.,polydimethylsiloxane) to fully cross-linked polymer. The fullycross-linked polymer is formed by a reaction between the functionalizedcross-linkable polymer and the cross-linking agent, for example, avinylsilylation reaction between vinyl-terminated polydimethylsiloxaneand polymethylhydrosiloxane optionally in the presence of a platinumcomplex catalyst. The ratio between non-cross-linkable polymer, e.g.,polydimethylsiloxane, and fully cross-linked polymer is sufficientlyeffective to provide structural reinforcement to the resultinginterpenetrating polymer networks, and is typically between about 0.1wt./wt. and about 9 wt./wt., preferably between about 0.43 wt./wt. andabout 2.33 wt./wt. The vinyl-terminated cross-linkable base polymer,e.g., polydimethylsiloxane base polymer, useful in the coatings of thepresent invention will have a weight average molecular weight (Mw) ofbetween about 10,000 and about 500,000 and preferably between about50,000 to about 250,000. Examples of this polymer include, but are notlimited to: Gelest Product Code No. DMS-V51, DMS-V52, DMS-V61, DMS-V71,etc., available from Gelest, Inc., Morrisville, Pa. 19067. The typicalmolecular structure of vinyl terminated polydimethyldisiloxane is thefollowing:

wherein n is defined by the molecular weight.

The cross-linkable siloxane polymer forms the matrix phase of thecoating on surface or surfaces of a medical device. Vinyl terminatedpolydimethylsiloxane reacts with polymethylhydrosiloxane cross-linker inthe presence of platinum catalyst under appropriate conditions; thevinyl terminated polydimethylsiloxane linear polymers are fullycross-linked to each other as the result of this reaction. The amount ofpolymethylhydrosiloxane cross-linker is in large stoichiometric excesscompared to vinyl terminated polydimethylsiloxane base polymer. It isbelieved that the extra SiH functions in the cross-linker react with theOH functions on the surface of the oxide layer of the medical devices,e.g., steel needles, to form Si—O—Fe bonds at elevated temperature.Covalent bonds thus created between the silicone coating and the deviceor needle surface, as the result of this reaction, result in theadhesive attachment of the coating to the metallic surface.

The polymethyhydrosiloxane cross-linkers, or cross-linking agents, usedin the practice of the present invention will have a weight averagemolecular weight (Mw) between about 1000 and about 3000, and preferablybetween about 1400 and about 2100. An example of this polymercross-linker includes, but is not limited to, Gelest Product Code No.HMS-991, HMS-992, available from Gelest, Inc., Morrisville, Pa. 19607.The typical molecular structure of the polymethyhydrosiloxanecross-linker is the following:

wherein n is defined by the molecular weight.

Polymethylhydro-co-polydimethylsiloxane can also be used as cross-linkeror cross-linking agent in the novel coatings of the present invention.Examples of this polymer include, but are not limited to, Gelest ProductCode No. HMS-301, HMS-501. The weight average molecular weight of thissiloxane polymer cross-linking agent will typically be between about 900and about 5,000, and preferably about 1,200 to about 3,000. The typicalmolecular structure of polymethylhydro-co-polydimethylsiloxane crosslinker is the following:

wherein n and m are defined by the molecular weight.

The non-cross-linkable siloxane polymer used in the lubricious coatingsof the present invention is preferably trimethylsilyl-terminatedpolydimethylsiloxane; which is a linear high molecular weightpolydimethylsiloxane polymer, and which does not contain reactivefunctional groups. This polymer provides a non-cross-linked phase in theresulting silicone coating, and is believed to disperse in the matrixphase made from the cross-linked cross-linkable siloxane. The weightaverage molecular weight of this polymer will typically be greater thanabout 200,000, preferably between about 200,000 to about 10,000,000, andmore preferably between about 400,000 to about 700,000. Examples of thispolymer include, but are not limited to, Gelest Product Code No.DMS-D-56, DMS-T62, DMS-T61, DMS-D72. The typical molecular structure ofthe non-cross-linkable siloxane polymer is illustrated below:

wherein n is defined by the molecular weight.

Catalyst

Bruce Karstedt of GE Silicone invented a highly active platinum catalyst(the “Karstedt catalyst”) at the beginning of the 1970's (U.S. Pat. No.3,775,452). Vinyl-terminated polydimethylsiloxane can react with apolymethylhydrosiloxane cross-linker in less than one minute at ambienttemperature with as little as 10 ppm of the Karstedt catalyst. It istypically difficult or impossible to use this catalyst in conventionalneedle production manufacturing processes because of its high rate ofcatalytic activity, and since the economics of conventional productionprocesses ideally and typically require up to a one week pot life forthe fully catalyzed silicone coating solution. The novel fast curingplatinum catalyst of the present invention has been developed to addressthis issue, and the resulting mixtures of this novel catalyst togetherwith the cross-linkable and non-cross-linkable silicone polymers of thepresent invention, e.g., vinyl-terminated polydimethylsiloxane andpolymethylhydrosiloxane, can be stable at ambient temperatures for morethan one week. The cross-linking reaction between the crosslinkablesilicone polymer and the cross-linking agent, for example,vinyl-terminated polydimethylsiloxane and polymethylhydrosiloxane, inthe presence of the novel catalyst of the present invention can beswitched on in less than 10 seconds at elevated temperature. The novelcatalyst of the present invention is prepared by reacting the Karstedtcatalyst with ethynylcyclohexanol according to Scheme 1 as seen below.The novel catalyst of the present invention provides greater controlover curing of the silicone coating solutions. This is conventionallyreferred to as “command cure”.

The novel catalyst of the present invention may be prepared in thefollowing manner. Karstedt catalyst in xylene solution is mixed with alow concentration of ethynylcyclohexanol in xylene solution at ambienttemperature for a sufficiently effective time to complete the reaction,e.g., a half an hour, and completion of the reaction is indicated by achange of the color of the reaction mixture, from clear to light brown.The resulting catalyst solution containing the novel catalyst of thepresent invention is ready to use in the preparation of the lubriciouscoating solutions of the present invention. The formula of the resultingplatinum complex catalyst (platinum divinyltetramethyldisiloxanecomplex) is:Pt[(CH₂═CH)(Me)₂Si]₂O.C₆H₁₀(OH)(C≡CH)

It should be noted that the resulting catalyst reaction mixture willcontain a small amount of the reaction productdivinyltetramethyldisiloxane. This component does not affect thecatalyst, and is a low boiling point component that is rapidly boiledoff. Accordingly, purification of the catalyst mixture to removedivinyltetramethyldisiloxane is optional, and it is believe that itspresence will not affect the cross-linking reaction of a cross-linkablesilicone polymer. The novel catalyst of the present invention isinhibited at low or ambient temperatures and activated at higher orcuring temperatures, that is, the catalyst is inactivated at lower orambient temperatures and activated at higher or curing temperatures.This allows for command cure (command cure catalytic action) of thecross-linkable components in silicone coatings to rapidly form coatingfilms at desired curing temperatures, and provides for long pot life.

Although the novel catalyst of the present invention is preferred andmost desirable in the coating compositions of the present invention, itis also possible to use conventional catalysts with these coatingcompositions. The conventional catalysts includeplatinum-cyclovinylmethylsiloxane complex (Ashby Karstedt Catalyst),platinum carbonyl cyclovinylmethylsiloxane complex (Ossko catalyst),platinum divinyltetramethyldisiloxane dimethyl fumarate complex,platinum divinyltetramethyldisiloxane dimethyl maleate complex and thelike and equivalents.

Solvent and Coating Mixing Procedure

The above-described silicone polymers and platinum catalysts, includingthe novel platinum complex catalyst of the present invention, aredispersed into organic solvents to form the novel lubricious coatingsolutions or compositions of the present invention. Both aromatic andaliphatic solvents can be used for the silicone dispersions, however,aromatic solvents are most commonly used for silicone dispersions.Typical examples of useful aromatic solvents include, but are notlimited to, xylene and toluene. Aliphatic solvents which are usefulinclude, but are not limited to, pentane, heptanes, hexane and theirmixtures. An example of an aliphatic solvent mixture is Exxon Isopar Ksolvent. The organic solvents are added at a concentration sufficient toprovide effective blending of the silicone polymer components into ahomogeneous coating solution. The total solvent concentration sufficientto be effective is typically between about 75 wt. % to about 99.5%, andis more typically between about 85 wt. % to about 98.5 wt. %, dependingupon the coating thickness requirement. Those skilled in the art willappreciate that the coating thickness can be engineered by changing thesolids content of the coating solution.

The following procedure as described utilizes conventional mixingequipment in typical production facilities. The coating compositions ofthe present invention may be preferably prepared in the followingmanner. Initially, a suitable organic solvent such as xylene is added toa conventional mixing vessel together with a platinum catalyst and mixedfor a sufficiently effective time, for example, up to about 10 minutesto form a solution. Then, a non-cross-linkable silicone polymercomponent such as trimethylsilyl-terminated polydimethylsiloxane andvinyl-terminated cross-linkable silicone polymer component such aspolydimethylsiloxane are dispersed into the solution for a sufficientlyeffective time; for example, for up to about two hours until fullyhomogeneous. A suitable organic solvent such as Isopar K solvent is thenadded to the solution, and the solution is further mixed for asufficiently effective time, for example, for about one hour prior tothe addition of a cross-linking agent such as polymethylhydrosiloxanecross-linker. Then, the cross-linking agent is added to the solution andthe solution is fully blended for a sufficiently effective time. Thelength of such time can be, for example, one additional hour after allof the components have been added to the mixing vessel.

Other conventional blending and mixing processes and equipment may beused to manufacture the novel silicone coating compositions of thepresent invention. For example, the sequence can be modified to someextent when using various other suitably effective conventional mixingequipment, such as a double planetary mixer. All of the components maybe mixed in one step in such equipment.

Although not necessarily preferred, in order to reduce VOC emissions, itis possible to formulate the lubricious coating compositions of thepresent invention in a less volatile organic solvent, an aqueous/organicsolvent mixture, or an aqueous solvent solution. This can be done bydone in a conventional manner similar to that used for low VOC polymericcoatings.

In the following paragraph the wt. % is the wt. % of total solid contentin the coating solution. The novel coating compositions of the presentinvention will contain sufficient amounts of the polymeric components,cross-linking agent, catalyst, and solvent to effectively provide asilicone coating having high lubricity and durability, a long pot life,and suitable for application in conventional coating processes usingconventional coating equipment. Typically, the amount of thenon-cross-linkable silicone polymer will be about 10 wt. % to about 90wt. % (total solids), more typically about 30 wt. % to about 70 wt. %(total solids), and preferably about 40 wt. % to about 60 wt. % (totalsolids). The amount of the cross-linkable silicone polymer willtypically be about 10 wt. % to about 90 wt. % (total solids), moretypically about 30 wt. % to about 70 wt. % (total solids), andpreferably about 40 wt. % to about 60 wt. % (total solids). The amountof the silicone cross-linking agent will typically be about 0.2 wt. % toabout 1.8 wt. % (total solids), more typically about 0.6 wt. % to about1.4 wt. % (total solids), and preferably about 0.8 wt. % to about 1.2wt. % (total solids). The amount of the platinum catalyst based upon thetotal solids in the novel lubricious silicone coating compositions(platinum element in total solids) of the present invention willtypically be about 0.0004 wt. % to about 0.0036 wt. %, more typicallyabout 0.0012 wt. % to about 0.0028 wt. %, and preferably about 0.0016wt. % to about 0.0024 wt. %.

The amount of organic solvent in the coating compositions of the presentinvention will typically be about 75 wt. % to about 99.5 wt. %, moretypically about 28 wt. % to about 99 wt. %, and preferably about 15 wt.% to about 98.5 wt. %. Those skilled in the art will appreciate that theamount of solvent present in the novel coating compositions of thepresent invention will vary with several factors, and that the solventquantity in the coating compositions will be selected to engineer anefficacious coating. The factors typically considered include the methodof application, the method of cure, the coating equipment utilized,ambient conditions, thickness, etc. It will be appreciated that each ofthe components of the coating compositions of the present invention mayconsist of blends of those components. For example, two or moredifferent molecular weight non-cross-linkable silicone polymers may beused, or two or more cross-linkable silicone polymers having differentfunctionalities and/or molecular weights may be used, etc.

Coating Process

The novel silicone lubricious coating compositions of the presentinvention are applied to one or more surfaces of a medical device, suchas a surgical needle, using conventional coating techniques andprocesses and conventional coating equipment. One example of coatingequipment that can be used to apply the coatings includes, but is notlimited to, simple dip coating tanks and in-line convection ovens forcuring. The coating compositions can also be applied by conventionalbrushing, rolling, or spraying processes, and any equivalent processes.The vinyl silylation addition cross-linking reaction can be completed(i.e., the coating can be cured) in-line by passing the coated devicethrough a drying oven for a sufficiently effective time. The curingtimes will vary, for example, from about 5 seconds to about one hour,and will vary with respect to parameters such as the cross-linkerconcentration, catalyst concentration, coating thickness, ambientconditions, device construction and material type, etc. However, thecure times can be as short as about 20 seconds at 450° C., or about 6seconds at 600° C. Flash cure (i.e., instantaneous or rapid cure) canalso be achieved with the present lubricious silicone coating containingthe novel catalyst of the present invention. Other conventional curingtechniques which can be utilized with the novel silicone coatingcompositions of the present invention include thermal (e.g., convectionheating), ultraviolet light, plasma, microwave radiation,electromagnetic coupling, ionizing radiation, laser, and the like. Priorto coating, the surfaces of the medical devices will be prepared in aconventional manner using conventional processes such aselectro-polishing, oxidation, ultrasonic cleaning, plasma etch, chemicalcleaning, and the like.

Test Procedures for Coating Performance

Coating performance for medical devices coated with the novelcompositions of the present invention can be tested with a variety ofconventional friction or adhesion tests. In the case of surgicalneedles, coating performance, durability and integrity are evaluatedusing a conventional needle penetration testing apparatus. A coatedsurgical needle is held using a mounting fixture on the apparatus, suchas self-locking tweezers or a similar holding device. The coated needleis then passed through a polymeric medium by the apparatus; thepolymeric medium is selected to be representative of general humantissue. Typically, approximately half of the needle length is passedthrough the medium and then retracted prior to the next pass. The testmedia may be a type of synthetic rubber (e.g., Duraflex™, manufacturedby Monmouth Rubber and Plastic Corporation, Monmouth, N.J.). The needlecan be passed through the penetratable material typically for about oneto about twenty times, more typically between about one to abouttwenty-five times, and most preferably between about one to about thirtytimes. The needle is then retracted from the media. The maximum force isrecorded for each pass and is used as a measure of the coatingperformance. Various attributes of coating performance can be testedusing these techniques, including durability and lubricity.

A typical test includes using 10 needles that are individually passedthrough the media 30 times each. The maximum force is recorded for eachpass and used as a measure of the coating performance. Typically thepenetration force increases with each successive pass as the coatingwears off from the needle.

As mentioned previously above, the medical devices that may be coatedwith the novel lubricious coatings include conventional medical devicessuch as surgical needles, hypodermic needles, catheters, surgicalprobes, endoscopes, syringes, scalpels, cutting blades, orthopaedicimplants, trocars, cannulas, and the like. The medical devices will beconstructed from conventional biocompatible materials including surgicalstainless steels, PTFE, glass, alloyed steels, refractory metal alloys,memory alloys, polymers, composites comprising metallic and non-metalliccomponents ingredients, combinations thereof, and the like. Thebiocompatible materials may include nonabsorbable materials andbioaborbable materials.

The following examples are illustrative of the principles and practiceof the present invention, although not limited thereto:

Example 1 Platinum Catalyst Synthesis Procedure

A novel platinum complex catalyst of the present invention was made inthe following manner. 60 grams of 1 wt. % Gelest SIP 6831 (2.2 wt. %platinum divinyl tetramethyldisiloxane complex, Karstedt catalyst)xylene were mixed with 60 grams of 1 wt. % ethynylcyclohexanol xylenesolution in a suitable mixing vessel for about 30 minutes at ambienttemperature until the mixture color changed to a light brown color. Thiscatalyst solution is referred to as Catalyst Formulation 1, and theplatinum complex catalyst (platinum divinyltetramethyldisiloxanecomplex) has the formula:Pt[(CH₂═CH)(Me)₂Si]₂O.C₆H₁₀(OH)(C≡CH)

Example 2 Viscosity Measurements on FullyCatalyzed Silicone SolutionReactivity/Stability Test

A pot life study was conducted using a silicone polymer coatingcomposition formulation as described below and outlined in Table 1.Three different catalysts were used in three different variations of theformulation, including the novel catalyst of Example 1 (CatalystFormulation 1), to investigate the effect of the catalyst upon the potlife of the coating composition.

TABLE 1 Silicone Polymer Coating Formulation 2 for Pot Life StudiesComponent Trade Name/Description Weight (g) Trimethylsilyl terminatedGelest DMS T72 300 poly dimethyl siloxane Dimethylvinyl silyl terminatedGelest DMS V52 300 poly dimethyl siloxane 0.01% Platinum catalystsolution 120 Trimethylsilyl terminated Gelest DMS HMS 991 6polymethylhydrosiloxane Solvent Xylene 1274

The viscosity of the formulations was measured over a period of time andthe results are summarized in Table 2. The viscosity measurement resultsof the formulations using conventional catalysts (Ashby and Karstedt,0.01% solution) were also included in this table for the purpose ofcomparison.

TABLE 2 Viscosity of Full Catalyzed Silicone Solutions, Using DifferentCatalysts (Catalyst Catalyst Formulation Time 1) Ashby Karstedt 0 min*4630 4630 4630 5 min 4827 5040 gel 30 min 4840 6253 1 hr 4840 10707 2 hr4910 gel 1 day 4920 2 day 4960 6 day 5050 12 day 5110 23 day 5310 28 day5360 40 day 5460 56 day 5470 *Measured on the solution without platinumcatalyst

The Karstedt catalyst gave less than 2 minutes pot life and the siliconesolution containing the Ashby catalyst gelled in less than 2 hours atambient temperature.

The formulation containing the catalyst of Example 1 (CatalystFormulation 1) gave less than a 5% change in viscosity after 6 days andincreased only 11% by the 28^(th) day. The viscosity difference wasminor and within the specification for typical silicone coatingsolutions.

Example 3 Molecular Weight Study of Non-Cross Linkable SiliconeComponent: Summary of Formulations

Uncoated Ethicon BV-175 surgical needles (8 mil diameter, no sutureattached, Ethicon, Inc., Somerville, N.J.) were coated with lubricioussilicone coating compositions. In the first set of experiments, theconcentration of the cross-linkable vinyl terminatedpolydimethylsiloxane, polymethylhydrosiloxane cross-linker, catalyst andsolvent were fixed, a series of non-crosslinkable trimethylsilylterminated polydimethylsiloxanes with different weight average molecularweights were used at the same concentration for this evaluation to studythe effect of molecular weight of the non-cross linkable component. Thedetails of these trimethylsilyl terminated polydimethylsiloxanes aresummarized in table 3-1.

TABLE 3-1 Summary of Different Grades of Trimethylsilyl TerminatedPolydimethylsiloxanes purchased from Gelest Inc. Gelest Molecular TradeViscosity Weight Name (cSt) (Mw) DMS-T51 100,000 139,000 DMS-T53 300,000204,000 DMS-T56 600,000 260,000 DMS-T61 1,000,000 308,000 DMS-T632,500,000 423,000 DMS-T72 20,000,000 >500,000Formulation 3A used Gelest DMS-T51 as non-cross linkable component andits details are summarized in table 3-2.

TABLE 3-2 Formulation 3A Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS-T51 1144 polydimethylsiloxane Dimethylvinyl silylterminated Gelest DMS-V52 1144 polydimethylsiloxane Catalyst solution as457.6 per Example 1 Trimethylsilyl terminated Gelest DMS 22.9polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent 2 ExxonIsopar K 8144Formulation 3B used Gelest DMS-T53 as the non-cross linkable componentand its details are summarized in Table 3-3.

TABLE 3-3 Formulation 3B Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS-T53 1144 polydimethylsiloxane Dimethylvinyl silylterminated Gelest DMS-V52 1144 polydimethylsiloxane Catalyst solution as457.6 per Example 1 Trimethylsilyl terminated Gelest DMS 22.9polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent 2 ExxonIsopar K 8144Formulation 3C used Gelest DMS-T56 as the non-cross linkable componentand its details are summarized in table 3-4.

TABLE 3-4 Formulation 3C Component Trade Name Weight (g) Trimethylsilylterminated Gelest 1144 polydimethylsiloxane DMS-T56 dimethylvinyl silylterminated Gelest 1144 polydimethylsiloxane DMS-V52 Catalyst solution457.6 as per Example 1 Trimethylsilyl terminated Gelest DMS 22.9polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent 2 ExxonIsopar K 8144Formulation 3D used Gelest DMS-T61 as the non-cross linkable componentand its details are summarized in table 3-5.

TABLE 3-5 Formulation 3D Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS-T61 1144 polydimethylsiloxane dimethylvinyl silylterminated Gelest DMS-V52 1144 polydimethylsiloxane Catalyst solution457.6 as per Example 1 Trimethylsilyl terminated Gelest DMS 22.9polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent 2ExxonIsopar K 8144Formulation 3E used Gelest DMS-T63 as the non-cross linkable componentand its details are summarized in table 3-6.

TABLE 3-6 Formulation 3E Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS-T63 1144 polydimethylsiloxane dimethylvinyl silylterminated Gelest DMS-V52 1144 polydimethylsiloxane Catalyst solution457.6 as per Example 1 Trimethylsilyl terminated Gelest DMS 22.9polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent 2 ExxonIsopar K 8144Formulation 3F used Gelest DMS-T72 as the non-cross linkable componentand its details are summarized in table 3-7.

TABLE 3-7 Formulation 3F Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS-T72 1144 polydimethylsiloxane Dimethylvinyl silylterminated Gelest DMS-V52 1144 polydimethylsiloxane Catalyst solution457.6 as per Example 1 Trimethylsilyl terminated Gelest DMS 22.9polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent 2 ExxonIsopar K 8144Formulation 3G was identical to Formulation 3F except for the type ofcatalyst used in the formulation and its details are summarized in table3-8.

TABLE 3-8 Formulation 3G Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS-T72 1144 polydimethylsiloxane dimethylvinyl silylterminated Gelest DMS-V52 1144 polydimethylsiloxane 0.02% Ashby catalyst0.05% Gelest 457.6 SIP 6832-2 in xylene Trimethylsilyl terminated GelestDMS 22.9 polymethylhydrosiloxane HMS-991 Solvent 1 Xylene 5087.4 Solvent2 Exxon Isopar K 8144Formulation 3H was also prepared with higher loading of organic solventIsopar K for a two layer coating study and the details are summarized inTable 3-9

TABLE 3-9 Formulation 3H Component Trade Name Weight (g) Trimethylsilylterminated Gelest DMS T72 960 polydimethylsiloxane Dimethylvinyl silylterminated Gelest DMS V52 960 polydimethyl siloxane Catalyst solutionper Example 1 384 Trimethylsilyl terminated Gelest DMS 19.2polymethylhydrosiloxane HMS 991 Solvent 1 Xylene 4269.1 Solvent 2 ExxonIsopar K 9408

Example 4 Molecular Weight Study of Non-Cross-linkable SiliconeComponents: Performance Evaluations

Uncoated BV175 needles (Ethicon, Inc.) were dipped into the coatingsolutions of Formulations 3A-3G by hand and the excess silicone coatingswere removed by compressed air. The coated needles were heated in aconventional convection oven at 195° C. for 30 minutes

Coating performance for medical devices coated with the novelcompositions of the present invention can be tested with a variety ofconventional friction or adhesion tests. In the case of surgical needlesfor this Example 4, coating performance, durability and integrity wereevaluated using a conventional needle penetration testing device. Eachcoated surgical needle was mounted and held in a mounting fixture on theapparatus such as g self-locking tweezers or a similar holding device.

The coated needle was then passed by the apparatus through a polymericmedium that was selected to be representative of general human tissue.Approximately half of the needle length was passed through the mediumand then retracted prior to the next pass. The test media used for thisexample was a type of synthetic rubber (Duraflex™, Manufacture byMonmouth Rubber and Plastic Corporation, Monmouth, N.J.). Each testincluded using 10 needles that were individually passed through themedia 30 times each. The maximum force was recorded for each pass andused as a measure of the coating performance. Typically the penetrationforce increases with each successive pass as the coating wears off fromthe needle.

Formulation 3A to 3F are identical to each other apart from themolecular weight of the non-cross linkable silicone. The averagepenetration force for the 1^(st), 10^(th), 20^(th) and 30^(th) pass of acoated needle for each formulation is summarized in Table 4-1.

TABLE 4-1 Needle Penetration Test: Example 4, (Formulations 3A to 3F,Trimethylsilyl- Terminated Polydimethylsiloxane with Different MolecularWeights) Penetration Force (g) Formulation 1st 10th 20th 30th 3A 29 5465 70 3B 23 41 50 55 3C 22 33 41 45 3D 21 31 38 42 3E 20 30 36 39 3F 1827 32 35

The needle penetration test results showed that lower molecular weighttrimethylsilyl-terminated polydimethylsiloxane (<200,000) gavecomparatively poor lubrication performance with substantially higherpenetration force required for insertion into the test media.

Needle penetration test results showed that conventional catalysts gavecomparable lubrication performance when used in the novel coatings ofthe present invention compared to the novel catalyst of the presentinvention (Example 1) with similar penetration force required forinsertion into the test media, as illustrated in Table 4-2.

TABLE 4-2 Needle Penetration Test: Example 4, (Formulation 3F and 3G,with Different Platinum Catalyst) Penetration Force (g) Formulation 1st10th 20th 30th 3F 18 27 32 35 3G 20 27 30 31

Example 5 Coating Process Optimization, Cure Time Study on the BestFormula

Uncoated BV175 needles (Ethicon, Inc.) were dipped into the coatingcomposition of Formulation 3F by hand and any excess silicone coatingcomposition was removed by compressed air. The coated needles wereheated at 195° C. for one minute prior to the application of a secondlayer of coating, using Formulation 3H, applied in a similar manner. Thecoated needles were divided into three sets and then cured at 195° C.for 2 minutes, 30 minutes and 7 hours, respectively, in a conventionalconvection oven to provide three sets of cured needles having threedifferent cure times, with the needles having two layers of coating.Penetration testing was performed on these three sets of needles asdescribed in Example 4. The results are from penetration testing doneusing 8 individual needles. The coated needles were penetrated into thetest media 30 times each. The average penetration force for each pass issummarized in Table 5.

TABLE 5 Needle Penetration Test: Example 5 (Cure at Different TimePeriods) Avg. Avg. Avg. Force (g) Force (g) Force (g) Penetration# 2minute cure 30 minute cure 7 hr. cure 1 16 +/− 1 16 +/− 1 18 +/− 2 10 21+/− 1 21 +/− 1 22 +/− 2 20 23 +/− 1 22 +/− 2 24 +/− 1 30 24 +/− 1 24 +/−3 25 +/− 1

-   -   Only minor differences were observed on the coated BV175 needles        having two layers of coating cured for different lengths of        time. This indicates the robustness of the coatings of the        current invention, wherein a wide range of curing times resulted        in almost identical performance. Coatings known in the art        typically demonstrate significant performance variability        depending upon the curing time.

Example 6 Production Run in Production Facility

Uncoated BV175 needles (Ethicon, Inc.) were coated with the coatingcomposition of Formulation 3F via a conventional dipping process andthen flash dried at 250° C. in a conventional furnace or oven forapproximately 20 seconds and taken up on a spool. The spool of needleswas then exposed to a temperature of 195° C. for 30 minutes. Penetrationtesting was performed as described in the previous Examples. The resultsare for penetration testing done using 10 individual needles. The coatedneedles were penetrated 20 times each.

The average penetration force for each pass is summarized in Table 6. Aset of Multipass™ coated Ethicon BV-175 needles was tested as thecontrol sample for the purpose of comparison, and the results are alsoincluded in Table 6.

TABLE 6 Needle Penetration Test: Example 6. Avg. Force (g) Avg. Force(g) Formulation 3F Prior Art Coating Penetration# Coating MulitpassCoated 1 15 +/− 3 17 +/− 1 10 23 +/− 3 30 +/− 2 20 27 +/− 3 35 +/− 3

As seen in Table 6, the needles coated with the novel coatingcompositions of the present invention (e.g., coated with the coatingsolution of Formulation 3F), which contain both cross-linked andnon-cross linked polydimethylsiloxane polymer, produced a coating thatis more durable than the needles coated with a prior art siliconecoating composition. The average force of the 10th penetration of theneedle with the coating of Example 3 (Formulation 3F) was seen to be23.3% less than the control coated needle; and the average of the 20thpenetrations was 22.9% less. The structural formation of the newcoatings (Formulation 3F) typically took less than 2 minutes. A curetime of 30 minutes was used for Example 4 and Example 6 to ensure theremoval of organic solvents, which is significantly less than the curetime required for the formation of the control coating (4 hr. attemperature of 195° C.).

The novel coatings and catalyst of the present invention have manyadvantages compared with the coatings and catalysts of the prior art.The coatings allow for precise control over the cross-linked polymernetwork structure, leading to consistency of the resulting coatings andthe consistency of the performance of coated devices, in particularcoated surgical needles. The coatings provide a unique polymeric networkstructure, which provides both lubricity and durability of the resultingsilicone coating. The catalyst provides command cured catalytic action,enabling the coating solution to form a film rapidly while possessingdesirably long pot life. The catalyst is inhibited at low or ambienttemperatures and uninhibited or reactivated at higher or curingtemperatures. The coatings and catalysts provide for more efficientcoating and curing processes.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

I claim:
 1. A catalyst solution for cross-linkable silicone polymercoatings, consisting essentially of platinumdivinyltetramethyldisiloxane ethynylcyclohexanol complex in xylenehaving the formula:Pt[(CH₂═CH)(Me)₂Si]₂O.C₆H₁₀(OH)(C≡CH), wherein in the combination ofsaid catalyst with a cross linkable siloxane formulation, there is lessthan a 5% change in viscosity after 6 days at ambient temperature.
 2. Acatalyst solution for cross-linkable silicone polymer coatings,consisting essentially of platinum divinyltetramethyldisiloxaneethynylcyclohexanol complex as a reaction product of a platinum divinyltetramethyldisiloxane and an ethynylcyclohexanol in xylene having theformula:Pt[(CH₂=CH)(Me)₂Si]₂O·C₆H₁₀(OH)(C≡CH), and other reaction products ofthe platinum divinyl tetramethyldisiloxane and the ethynylcyclohexanol,wherein in the combination of said catalyst with a cross linkablesiloxane formulation, there is less than a 5% change in viscosity after6 days at ambient temperature.